1. Field of the Invention
Embodiments of the present invention are directed to photoconductors, and are specifically directed to photoconductors comprising dodecyl/tetradecyl glycidyl ether (DGE), octyl/decyl glycidyl ether (OGE), or combinations thereof in the charge transport layer, wherein the OGE or DGE are added to improve resistance to crazing, cracking and crystallization in the charge transport layer.
2. Description of the Related Art
A laminate photoconductor consists of a charge generation layer (CGL) and a charge transport layer (CTL) typically with the CTL as the outer layer. A CTL usually is comprised of a hole transport material and a polymer binder. The surface of a photoconductor is required to be smooth and free of any cracking/crazing lines in order to produce good quality prints. However, the integrity of a photoconductor surface can be destroyed or damaged by the touch of a human hand in some cases, which can result in CTL crazing/cracking. Within a solvent-coated charge transport layer, internal stress can build up during the drying process. As a result of this stress, cracking or so-called crazing in a charge transport layer may occur when the surface is touched by a human hand or finger, or contacted with certain chemicals. These cracking or crazing lines are permanent and cause print defects. The photoconductor is found either in a printer or a printer cartridge depending on the design of the printing system.
The sensitivity of a layered photoreceptor depends on all layers involved, including the charge generation and the charge transport layers. In a charge transport layer, the mobility of a charge transport molecule and the travel distance of a carrier are critical to the discharge of a photoreceptor. Increasing the concentration of charge transport molecule usually results in lowered discharge. However, depending on the structure of the binder and the charge transport molecule, crystallization may occur if the concentration of the charge transport molecule is increased beyond a certain point. Crystallization results in increased residual discharge and image defects, both of which are undesirable.
One approach to address the issue of CTL crazing/cracking and crystallization is to selectively use specific charge transport molecules, or a mixture. Some charge transport molecules inherently have superior CTL crazing/cracking resistance and a low tendency towards crystallization. For example, a charge transport layer containing p-(diethylamino)benzaldehyde diphenylhydrazone (DEH) at various loadings exhibits superior crazing/cracking resistance. Some fluorene derivatives also exhibit excellent cracking resistance and have little tendency to crystallize when formulated in a charge transport layer. Other conventional charge transport layers comprise mixtures of two or more types of charge transporting small molecules such as diamines (e.g. commonly used TPD), triphenylamines and triphenyl methanes. Crazing or cracking of the charge transport layer is effectively eliminated as a result.
Another common approach to enhance crazing/cracking resistance is to dope additive(s) into the charge transport layer. A commonly used additive for such purposes is a plasticizer, for example, diethyl phthalate or branched aliphatic esters. Also, benzotriazole and a branched hydrocarbon have been utilized in the charge transport layer to improve crazing/cracking performance. However, using additives may degrade the electrical and mechanical performance of the photoconductor.
Accordingly, there is a need for improved photoconductors comprising charge transport layer with additives operable to control crazing, cracking or crystallization in the charge transport layer while maintaining the electrical and mechanical properties of the photoconductor.